THE FLIGHT The turning point came with two innovations: the Very Long Range (VLR) Consolidated B-24 Liberator and the escort carrier. Coastal Command modified Liberators to extend their range to 2,500 miles, allowing them to reach the air gap and remain on station for eight hours. The first VLR squadron (No. 120) was joined by others, but the breakthrough was slow. At the end of March 1943, only twenty VLR aircraft were operational. By May, the combination of VLR Liberators, escort carriers such as USS Bogue (CVE-9), and hunter-killer support groups had turned the tide. In "Black May" 1943, the U-boats were hunted from the sky and sea; forty-one were destroyed that month, and Doenitz temporarily withdrew his wolf packs from the North Atlantic. The Admiralty's War at Sea records show that air patrols, even when they did not score kills, forced U-boats to remain submerged, exhausting their batteries and denying them the speed to attack.